Tie line



June 26, 1945. L J, BOWNE 2,379,061

' TIE LINE Filed July 12, 1944'- L INE INVENTOR LJ BOWNE AT TORNEVPatented June 26, 1945 TES TNT OFFICE TIE LINE Application July 12,1944, Serial No. 544,555

6 Claims.

This invention relates to what are called private branch exchangetie-line systems, that is, lines interconnecting two private branchexchanges and. more particularly to an improved and simplified ring-downcircuit of this character.

In circuit arrangements, for this type of service which have beenheretofore used, means have been provided for automatically removing arepeating coil normally connected in the line, when ringing current isconnected to the line on outgoing calls, which removal has beenaccomplished by means of an alternating current relay actuated by theringing current which in turn controls another relay to open aconnection for the repeating coil and establish through connections forthe line conductors to permit the ringing current to pass directly outover the line. In such an arrangement when the ringing key is operated,and ringing current flows over the line, a substantial charge is builtup between the line conductors, due to the normal distributed capacityof the line, and when the ringing key is released and ringing ceases arelatively high potential surge from the charged line flows back intothe switchboard and may cause objectionable clicks in any connectedreceiver.

An object of the present invention is to guard against objectionableclicks when outgoing ringing current is disconnected from the line.

A feature of the invention whereby the foregoing object is obtainedresides in providing means, controlled by an outgoing ring, from eitherend of the line, for translating a repeating coil, normally included inthe line thereat, to constitute a low-pass filter for preventingundesirable clicks caused by a line discharge when the ringing currentis removed.

Another feature of the invention resides in such an arrangement ofcircuits at each end of the line that reliable and satisfactoryoperation is obtained with less and cheaper apparatus than heretoforeemployed in circuit arrangements of this character.

The invention will be understood from the following description whenread in connection with the accompanying drawing,

Fig. 1 of which shows one end of a tie-line arranged in accordance withthe invention and extending between two private branch exchanges; and

Fig. 2' is a schematic showing of the connection of the repeating coilduring an outgoing ring.

Assuming an outgoing call from the private branch exchange, theoperator, after inserting the plug I in jack 2 of the line, operates theringing key 3 to connect alternating ringing current to the line,whereupon relay 4 operates in a circuit including the lower or ringconductor of the line, unilaterally conducting device 5, winding of therelay 4, condenser 6 and the right-hand winding 1 of repeating coil 8 tothe upper or tip conductor of the line.

Relay 4, in operating, closes its upper contacts 10, thereby joining thelower terminals of windings l and 9 of the repeating coil and atcontacts I l connects the lower or ring conductor of the line through tothe ring spring of the jack 2. With contacts l8 and it closed windings land 9 of the repeating coil are connected in series with the upper ortip conductor of the line and the lower or ring conductor is connectedthrough to the jack thus forming a T-section of a low-pass filter asshownin Fig. 2 in which the windings i and 9 form the series inductanceelement and condensers l2 and I3, in parallel, the shunt capacity.

It will be understood that windings i and 9 are so connected that whenthey are in series with the line, they are inductively aiding withrespect to each other.

With relay 4 operated, i. e., when ringing current is connected to theline the filter arrangement, above described, has a negligibleattenuating effect on the outgoing ringing current, but when the ringingkey is released, thus disconnecting ringing current from the line, thisarrangement prior to the release of relay 4, offers a high seriesimpedance and a low impedance bridge to surges due to a capacitydischarge from the line which, otherwise, might cause objectionableclicks in the operators receiver.

During the ringing interval, operation of relay 4 also closes itscontact M to disconnect the ringup line relay I5, and its associatedunilaterally conducting devices, from their normal connection acrosscondenser l2,

Further, operation of relay 4 on an outgoing ring, removes at itscontacts H5 a resistance ll, which is normally connected acrosscondenser I3, for the purpose of reducing the load on the ringingcurrent supply. 4

On an incoming ring, relay 15 operates and locks over its upper contactsand, by closing its contacts 18, lights the line lamp IS in theswitchboard. Relay !5, in operating, also opens its mally closedcontacts 20 thus opening at another point the circuit across condenser[3 which includes resistance [1, which, however, performs no usefulfunction at this time.

In the case of a rering while the cord circuit is connected to the jack2, relay l5 operates but does not lock due to the fact that its lockingwinding is short-circuited at local contacts 2| of the jack 2. Contactsare also opened at this time which disconnect the resistance I! from itsnormal connection across condenser I3 to cause a supervisory relay inthe cord circuit (not shown) to light a supervisory lamp in the cord asa signal to the operator. The line lamp L9 ,also lights on a rering butin this case its value is negligible.

What is claimed is:

1. In a telephone system, in combination, a private branch exchange, aswitchboard thereat, an inductive device at said exchange comprising atwo-winding transformer and a pair of condensers, a two-way ring-downie-line 'terrninating in series with one of said windings and one ofsaid condensers, the other winding and condenser being seriallyconnectedto line terminals of said switchboard, a pair of relays eachadapted to respond to ringing current, a third, condenser, a first oneof said relays being serially connected with the third condenser inshunt to the condenser in the switchboard side of said inductive deviceand the second relay being normally connected in shunt to thecondenserin the line side of said inductive device under control of said firstrelay, a, resistance normally connected, .under joint control of bothrelays, in a circuit in shunt to the condenser in the switchboard sideof the inductive device, and means responsive to operation of said firstrelay, for connecting the line through to the switchboard with the twocoil windings in series with one side thereof and the said pair ofcondensers in a parallel bridge between the mid-point of said connectedwindings and the other side of the line.

2. In a telephone system, a switchboard, a tieline, .a two-windingrepeating coil for inductively connecting said tie-line to saidswitchboard, a condenser in series with each of said windings, a ringingresponsive relay connected to said line, means .at said switchboard forapplying ringing current to said line to operate said relay, and meansresponsive to operation of said relay for connecting one side of theline through .to the switchboard .in series with said two coil windings,directly connecting the other side of the line through to theswitchboard and for connecting said two condensers in .parallel betweensaid other side .of the line and a point intermediate said two windings.

3. 111a telephone system, a switchboard, a tieline, a two-windingrepeating coil for inductively connecting said tie-line to saidswitchboard, a condenser in series with each of said windings, aresistance shunting the condenser in the switchboard side of saidrepeating cell, a ringing responsive relay connected to said line, meansat said switchboard for applying ringing current to said line to operatesaid relay, and means responsive to operation of said relay forconnecting one side of the line through to the switchboard in serieswith said two coil windings, directly connecting the other side of theline through the switchboard and for connecting said two condensers inparallel between said other side of the line and a point intermediatesaid two windings, and other means responsive to operation of said relayfor disconnecting said resistance from its shunt connection to saidcondenser.

4. Ina telephone system, a switchboard, a tieline, a two-windingrepeating coil inductively connecting said tie-line to said switchboard,a condenser in series with each of said coil windings, a first relayconnected in parallel with the condenser in the switchboard side of saidrepeating coil, means at said switchboard for applying ringing currentto the line to operate said first relay, means responsive to operationof said first relay for connecting one side of the line through to theswitchboard in series with said two coil windings, directly connectingthe other side of the line through to the switchboard, and forconnecting said two condensers in parallel between said other side of-the line and a point intermediate said two windings, a second relayconnected in (parallel with the condenser in the line side of said r epeating coil and responsive to ringing current incoming over said lineand other means also responsive to operation of said first relay fordisabling said second relay.

5. In a telephone system, a switchboard, a line, a two-winding repeatingcoil inductively coupling said line to said switchboard, a condenser.inseries with each of said coil windings, a relay connected in shunt tothe condenser in the-switchboard side of said repeating coil andresponsive to ringing current applied to the line at the switchboard foreffectively translating said repeating coil and associated condensers toconstitute -a ,T-section of a low-pass filter in said line.

6. In a telephonesystem, a switchboard, a tieline, a two-windingrepeating vcoil inductively connecting said line to the switchboard, acondenser in series with each of said coil windings, a first relayconnected in parallel with the condenser in the switchboard side of saidrepeating coil, means for applying ringing current to the line at theswitchboard to operate said relay, means responsive to operation of.said first relay for connectingone side of the line through to-theswitchboard in series with said two coil windings, directly connectingthe other side of the line through to the switchboard and for connectingsaid two condensers in parallel between said other sidepf the line and apoint intermediate the two windings, a second relay responsive toringing current connected in parallel with thecondenser in the line sideof said repeating coil, a resistance also shunting the condenser in theswitchboard side of said repeating coil, means "responsive to operationof said firstrelay for disabling saidsecand relay, and means responsiveto operation of either one of said relays for disconnecting saidresistance.

LANGFORD J. BOWNE.

